It is known to use overbased detergents in an oil of lubricating viscosity to reduce engine wear and improve cleanliness. Overbased detergents include sulphonates, salixarates or salicylates, and they provide alkalinity to neutralize sulphur-containing acids produced from the combustion of carbonaceous fuels. These detergents are prepared by a number of low and high temperature processes. However, the preparation of a highly overbased detergent is difficult because the in-process viscosity and final viscosity tend to be too viscous and the final product is not soluble or lacks clarity or becomes too viscous to be readily handle-able.
U.S. Pat. No. 6,444,625 (Muir et al.) discloses a method for preparing a handle-able overbased metal sulphonate detergent having a TBN of 400 or more, and having a viscosity of at least 180 mm2s−1 (cSt) at 100° C. The process for preparing the overbased sulphonate detergent requires a solvent system containing a hydrocarbon solvent and an alcohol with 1 to 4 carbon atoms. However, the hydrocarbon solvent is known to be environmentally unfriendly requiring safe storage and disposal of waste.
It would be desirable to have a process for preparing an overbased metal detergent that is handle-able, environmentally friendly, and substantially free of hydrocarbon solvent, in a cost effective manner. The present invention provides a process for preparing an overbased metal detergent that is handle-able, environmentally friendly, and substantially free of hydrocarbon solvent, in a cost effective manner.